Shaft positioning device



April 1954 M. L. CAMPBELL 3,130,594

' SHAFT POSITIONING DEVICE Filed June 25, 1962 IN VEN TOR. Me/w'n L. Campbell .4 ffarneys United States Patent "ice 3,139,594 SHAFT PDSITIGNING DEVICE Meivin L. Campbell, Marion, Iowa, assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of Iowa Filed June 25, 1962, Ser. No. 284,887 5 Claims. ((31. 74-84) This invention relates generally to shaft positioning devices and, more particularly, to shaft positioning devices which translate uniform rotary motion into intermittent rotary motion.

There are in the prior art many applications wherein it is necessary to angularly position a shaft. In some cases it is necessary to rotate the shaft in discrete angular steps. For example, in radio gear where it is desired to automatically select different frequency channels, a shaft is frequently caused to rotate in discrete angular steps, whereby switches, such as wafer switches located on such shaft, are rotated until a predetermined angular position of a shaft is reached. When such predetermined angular position of the shaft is obtained the contacts of the rotating wafer switches satisfy a predetermined electrically coded condition whereby the power source causing the rotation of the shaft is disconnected. Such switches are known, generally, in the art as seeking switches.

In some forms of prior art shaft positioning structures, the prime mover functions to rotate the shaft in a continuous manner to its newly selected position. In other instances, there is provided between a continuously rotating prime mover and the shaft to be positioned, an intermediate means which functions to translate the continuous rotary movement of the prime mover into intermittent rotary motion. Two primary advantages of translating the uniform rotary motion of the prime mover into intermittent rotary motion are as follows. The first advantage is that the angular positions of the shaft which is to be positioned are predetermined in accordance with the discrete angular steps of the intermittent rotary motion. Such definiteness of angular positions occurs as a result of the use of gearing mechanism in the motion translating structure. The second principal advantage is that the intermittent rotary motion provides a dwell in each of its angular positions so that if switches are actuated therewith to control a seeking switch, for example, ample time will be provided for control circuits to respond to the setting of said switches in accordance with a given angular position of the rotating shaft.

The prior art devices which translate uniform rotary motion into intermittent rotary motion are by and large comparatively complicated devices involving rather complex escape type mechanisms.

It is an object of the present invention to provide a relatively simple, yet reliable, shaft positioning device which will translate a uniform rotary motion supplied thereto into an intermittent rotary motion consisting of a predetermined finite number of steps per revolution, with a dwell between each step.

Another object of the invention is to provide a shaft positioning device capable of translating uniform rotary motion into intermittent rotary motion in which the shaft is caused to assume discrete angular positions with a high degree of accuracy.

A third purpose of the invention is the improvement of shaft positioning devices, generally.

In accordance with the invention, an input gear is mounted on a rotatable shaft by means of a spring, such as a torsion spring, so that the input gear can rotate while the shaft is restrained from rotating. A stop wheel having teeth around its perimeter is mounted concentrically upon the shaft and is rigidly affixed thereto. A cam is also mounted upon the shaft and operates in co-opera- 3,136,594 Patented Apr. 28, 1964 tion with a pair of pawls mounted upon a cam follower. The pawls are positioned near the perimeter of the stop wheel and are approximately removed from each other around the perimeter of said stop wheel. As the cam functions to move the cam follower and the pawls back and forth across the face of the stop wheel in a transverse manner, first one pawl and then the other engages the teeth of the stop wheel. However, the posi tion of the pawls with respect to the perimeter of the stop Wheel and the spacing between the teeth on the stop wheel are such that each time the pawls are moved in and out of the teeth, the stop wheel escapes one half of a notch, angularly. It is to be noted that the cam is mounted rigidly on the input gear and is concentrically positioned with respect to the rotatable shaft so that the cam rotates with the input gear even though the shaft may be restrained. Such rotation of the cam causes the movement of the pawls and the cam follower back and forth in their transverse motion to permit rotation of the rotatable shaft a discrete angular amount each time one of the pawls is removed from the path of the teeth of the stop wheel.

The above and other mentioned objects and features of the invention will be more fully understood from the following detailed description thereof when read in conjunction with the drawing in which:

FIG. 1 shows an exploded perspective view of the invention; and

FIG. 2 shows a view of the stop Wheel, the pawls, and the cam follower, and illustrates the coaction therebetween.

Referring now to the structure of FIG. 1, rotary motion is applied to the input gear 11 by any suitable means such as motor 26, which is coupled to said input gear 11 by means of shaft 27 and gear 28. Such rotary motion may be uniform in nature. The input gear 11 is mounted securely by suitable means, such as friction means, to the casing 10 which contains a torsion spring 29 therein. One end of the torsion spring is rigidly aflixed to the casing 10 and the other end is rigidly afixed to the rotatable shaft 18. It is to be noted that the casing 10 and thus the input gear 11 are rotatable even though the shaft 18 is restrained since the only connection between the input gear 11 and the rotatable shaft 18 is the torsional spring 29.

A cam 12 is mounted upon the input gear 11, such that it can rotate with said input gear '11. However, the cam 12 is not secured to the shaft 18 so that it, like the input gear =11, can be rotated while the shaft 18 is restrained from such rotation. Around the perimeter of the cam 12 is a series of lobes, such as lobe 23. These lobes are employed to drive the pawl and cam follower unit 14 back and forth in a transverse motion to permit escapement of the stop wheel 13 in a manner vto be described later. It is to be noted that the pawl and cam follower unit 14 comprises a plate 30 having a slot 22 therein through which passes the shaft 18. At each end of the plate 30 there is located a pawl, such as pawls 15 and 16. The spacing between these two pawls preferably is slightly more than the diameter measured from the peak of one lobe to the valley mid-way between two lobes diametrically oppositely positioned on the cam. Also, as will he explained later, the position of the pawls 15 and 16 are such that when a peak of a lobe on the cam wheel 12 is passing under one of the pawls 15 or 16, the other pawl is passing midway between two peaks of the lobes of the cam wheel 12. 1

The stop wheel 13, as can be seen from the drawing, is mounted concentrically upon the shaft '18 and is rigidly afiixed thereto so that it must rotate with the shaft 18. Around the circumference of the stop wheel 13 there are a plurality of uniformly spaced teeth.

It is to be noted that the slot 22 of the plate 30 rides on, and is guided by, the shoulder 21 of the cam follower bushing 17, which is freely rotatable on the shaft 18. A pin 20 is mounted on the fixed reference point, such as the frame 19 of the structure and functions to keep the pawl and cam follower 14 and the bushing 17 from rotating.

In FIG. 2 the relationship between the pawls 15 and 16 and the teeth of the stop wheel 13, can be more clearly seen. More specifically, in FIG. 2 it can be seen that the tooth 25 is engaged with pawl 16, thus preventing rotation of the shaft 18. On the other hand, the pawl 15 has been moved out to the right beyond the tips of the teeth of stop wheel 13 so that it cannot impede the rotation of said stop wheel. However, as the input gear 11 (FIG. 1) and the cam 12 is caused to rotate, a lobe on the cam 12, such as lobe 23, will engage the pawl 16 and push it to the left in FIG. 2 so that the tooth 25 will be released therefrom and the stop wheel 13 will be caused to rotate by the torsional spring 29 in -a clockwise direction. However, when the cam 12 pushed the pawl 16 to the left of FIG. 2 it, of course, also caused the pawl 15 to move to the left so that when the tooth 25 is released from the pawl '16 and the stop wheel 13 rotates, the said stop wheel 13 will only rotate until the tooth 32 is caught on the pawl 15, thus permitting the rotatable shaft 18 -to rotate only a discrete angular dis- .tance.

From FIG. 2 it is apparent that the amount of angular rotation in each discrete step of the rotatable shaft 13 is approximately half the distance between the peaks of two adjacent teeth. However, by the proper positioning of the pawls 15 and 16, alternate discrete steps can be made to be different. However, the sum of any two discrete steps will equal the angular distance between the peaks of two adjacent teeth.

To incorporate the shaft positioning device described above, in a complete and self-contained system, a power source and a seeking switch (not shown) can be added. The seeking switch, which is well known in the prior art, could be coupled to the output shaft and would function to shut off the power source when the correct position of the shaft is obtained.

It is to be noted that the form of the invention shown and described herein is but a preferred embodiment thereof and that various changes may be made in the specific design of the various components without departing from the spirit or the scope thereof.

1 claim:

1. Means for converting continuous rotary motion into intermittent rotary motion comprising a rotatable shaft, input drive means mounted rotatably on said shaft, means which drive said input drive means, static energy storage means connecting said input drive means to said shaft and constructed to create a torque upon said shaft as said input drive means is rotated, cam means rigidly mounted on said input drive means and constructed to rotate therewith, stop wheel means mounted rigidly on said shaft and having a plurality of teeth positioned around its perimeter, cam follower means including first and second pawl means positioned at different positions near the perimeter of said stop wheel means and moved into and out of the path of the teeth of said stop wheel means as said cam follower is activated by said cam means to cause said stop wheel to advance by discrete angular distances in response to the torque supplied to said rotatable shaft, said pawl means being relatively positioned to cause one pawl means to be near the midpoint between two adjacent teeth of said stop wheel means when the other pawl means is in contact with a tooth of said stop wheel means.

2. Means for converting continuous rotary motion into intermittent rotary motion in accordance with claim 1 in which said static energy storage means comprises a torsion spring wound around the rotatable shaft with one end thereof secured to said rotatable shaft and the other end thereof secured to said input drive means.

3. Means for converting continuous rotary motion into intermittent rotary motion in accordance with claim 1, comprising guiding means constructed to cause said cam follower means to move transversely across the face of said stop wheel means in response to rotation of said cam means.

4. Shaft positioning means for positioning a rotatable shaft in any one of a predetermined number of discrete angular positions comprising a rotatable shaft, input drive means mounted rotatably on said shaft, means which drive said input drive means, energy storage means connecting said input drive means to said rotatable shaft and constructed to create a torque upon said shaft as said input drive means is rotated, cam means rigidly mounted on said input drive means and constructed to rotate therewith, stop wheel means rigidly and concentrically mounted upon said rotatable shaft and constructed to have a plurality of teeth around the perimeter thereof, cam follower means having first and second pawl means thereon which are moved transversely back and forth across the face of said stop wheel in response to rotation of said cam means, the said first and second pawl means being positioned near the perimeter of said stop wheel and moved alternately into and out of the path of said stop wheel means as said cam follower is activated by said cam means to cause said stop wheel to advance by discrete angular distances in response to the torque supplied to said rotatable shaft, said pawl means being positioned to cause one pawl means to be near the midpoint between two adjacent teeth of said stop wheel means when the other pawl means is in contact with a tooth of said stop wheel means.

5. Shaft positioning means in accordance with claim 4 in which said energy storage means comprises a torsion spring wound around the rotatable shaft with one end thereof secured to said rotatable shaft and the other end thereof secured to said input drive means.

References Cited in the file of this patent UNITED STATES PATENTS 277,849 Park May 15, 1883 416,354 Bulley Dec. 3, 1889 1,229,301 Loe June 12, 1917 FOREIGN PATENTS 438 Great Britain Jan. 8, 1892 

1. MEANS FOR CONVERTING CONTINUOUS ROTARY MOTION INTO INTERMITTENT ROTARY MOTION COMPRISING A ROTATABLE SHAFT, INPUT DRIVE MEANS MOUNTED ROTATABLY ON SAID SHAFT, MEANS WHICH DRIVE SAID INPUT DRIVE MEANS, STATIC ENERGY STORAGE MEANS CONNECTING SAID INPUT DRIVE MEANS TO SAID SHAFT AND CONSTRUCTED TO CREATE A TORQUE UPON SAID SHAFT AS SAID INPUT DRIVE MEANS IS ROTATED, CAM MEANS RIGIDLY MOUNTED ON SAID INPUT DRIVE MEANS AND CONSTRUCTED TO ROTATE THEREWITH, STOP WHEEL MEANS MOUNTED RIGIDLY ON SAID SHAFT AND HAVING A PLURALITY OF TEETH POSITIONED AROUND ITS PERIMETER, CAM FOLLOWER MEANS INCLUDING FIRST AND SECOND PAWL MEANS POSITIONED AT DIFFERENT POSITIONS NEAR THE PERIMETER OF SAID STOP WHEEL MEANS AND MOVED INTO AND OUT OF THE PATH OF THE TEETH OF SAID STOP WHEEL MEANS AS SAID CAM FOLLOWER IS ACTIVATED BY SAID CAM MEANS TO CAUSE SAID STOP WHEEL TO ADVANCE BY DISCRETE ANGULAR DISTANCES IN RESPONSE TO THE TORQUE SUPPLIED TO SAID ROTATABLE SHAFT, SAID PAWL MEANS BEING RELATIVELY POSITIONED TO CAUSE ONE PAWL MEANS TO BE NEAR THE MIDPOINT BETWEEN TWO ADJACENT TEETH OF SAID STOP WHEEL MEANS WHEN THE OTHER PAWL MEANS IS IN CONTACT WITH A TOOTH OF SAID STOP WHEEL MEANS. 